**1. Introduction**

Pests and diseases are estimated to cause 60% losses in cotton production throughout the world [1]. A successful control strategy requires integrated pest management (IPM) that prevents or suppresses damaging populations of insect pests by applying the comprehensive and coordinated integration of multiple control tactics, including chemical, cultural and biological methodologies.

Synthetic insecticides are mainly used on cotton to control insect pests rapidly [2], and farmers opt for insecticides as the first line of defense [3]. Since the development of synthetic insecticides after World War II, they have been extensively used in agriculture due to their efficiency in pest control and yield increment of many crops [4]. Cotton has been reported to receive more chemical control than

most other arable crops [5]. Cotton uses up to 60% of all commercialized agrochemicals globally [6]. Various insect pests and beneficial insects coexist in a cotton ecosystem; however, insecticides have reduced the impact of beneficial insects [7]. As one of the management tools for pests, synthetic insecticides can be used as part of integrated pest management to promote sustainable pest control methods [8]. When synthetic insecticides such as organophosphate (1960s), carbamates (1970s), and pyrethroids (1980s) were introduced, they had an impact on agricultural pest control and resulted in high yields [9].

Although chemical control remains a key method to control targeted pests, a controversy has surfaced regarding the use and abuse of pesticides [9]. The diversity of pests found on cotton requires serious control, mostly with pesticides, which subsequently has a negative impact on natural enemies and the environment [10]. The continuous use of synthetic chemicals to protect crops may also result in resistance to insecticides in pest populations [3]. Combining chemical and biological controls is important for integrated pest management; however, this has not been entirely explored due to, among others, the insufficient information on the insecticide tolerance or resistance of natural enemies [11]. The development of integrated pest management strategies is required to reduce insecticide use and maximize the impact of natural enemies.

Biological control includes introducing a natural enemy or living organisms [12], and cultural control focuses on manipulating the environment to reduce the pest's populations [13]. Pest management has evolved to include integrated pest management that focuses on biological control strategies, including biopesticides. It has been widely reported that chemical pesticides have a negative impact on the environment; therefore, efforts have been made to minimize their use in controlling insect pests. Biopesticides are commonly used to manage agricultural pests through specific biological effects [14] compared to wider control of synthetic pesticides. They contain organisms or substances derived from natural resources in nature and have inhibitory effects on insect pests.

Biopesticides are cheaper, take less time to develop [15], and are naturally less toxic to humans and the environment [16] compared with synthetic pesticides. They are mainly categorized into biochemical, plant, and microbial pesticides [17–19]. Biochemical pesticides include plant extracts, pheromones, plant and insect growth regulators that control pests by non-hazardous mechanisms [20]. Plant pesticides, also known as plant-incorporated protectants, include genetically modified crops using protein from the bacterium *B. thuringiensis* [15]. Microbial pesticides consist of viruses, fungi, and bacteria [21]. Biopesticides form only around 5% of the global pesticides [22], while microbial pesticides account for over 75% worldwide [23]. This chapter provides an overview of microbial-based products *B. thuringiensis*, *B. bassiana*, *H. armigera* nucleopolyhedrovirus, *M. rileyi* and their application to control cotton pests. The chapter further explores the constraints and opportunities for the use of these biopesticides.

#### **2.** *Bacillus thuringiensis*

*Bacillus thuringiensis* (Bacillaceae) is a spore-forming gram-positive bacterium that produces poisonous insecticidal crystal proteins used on more than 3 000 different insects [24, 25]. The bacterium commonly lives in soil, water, plants and dead insects [26]. It was first isolated by Shigetane Ishiwatari in 1901 and first used commercially in the 1920s [27]. *B. thuringiensis* accounts for 95% of the biopesticide market worldwide [28]. The bacterium plays a significant role in biological control because it is the most widely used microbial control agent [19]. Different strains

*Role of Microbial Biopesticides as an Alternative to Insecticides in Integrated Pest Management… DOI: http://dx.doi.org/10.5772/intechopen.100400*


#### **Table 1.**

*Summary of some studies on the control of cotton pests using* Bacillus thuringiensis.

of *B. thuringiensis* have been produced with different spectrums of activity [29]. Although there are massive spectrums with different cry toxin genes, kurstaki and aizawaï are the only two *B. thuringiensis* subspecies developed into products used to control lepidopteran pests [30]. *B. thuringiensis* commonly attacks larval stages of different insects rather than adults or other stages [31, 32]. As a target-specific pathogen, *B. thuringiensis* only attacks the target insects [33] without disturbing non-target insects and natural enemies [32, 34]. *B. thuringiensis* does not kill the target pest on contact but through disruption of the midgut tissue of the insect [31]. Therefore, it is difficult for the pathogen to attack those insects that feed inside the plant [32]. *B. thuringiensis* toxins have shown well-documented toxicity against various insects, including Lepidoptera, Diptera, Hemiptera, Coleoptera, and nematodes [35–40]. In cotton, *B. thuringiensis* has been widely reported as a biopesticide to control various insect pests [27, 41, 42]. **Table 1** provides an overview of some studies conducted to control some cotton pests using *B. thuringiensis*.

### **3.** *Beauveria bassiana*

*Beauveria bassiana* (Ascomycota: Cordycipitaceae) is a fungus that grows naturally in soils. It is one of the commercial alternatives to chemical insecticides [52]. Its strains have been used as the active ingredient in several biopesticides to control a diversity of agricultural pests [53]. The genus *Beauveria* contains at least 49 species, of which approximately 22 are considered pathogenic [54]. Notwithstanding its importance as a biological control agent, *B. bassiana* is also an organism used to examine fungal growth and development, such as host-pathogen interactions [55, 56]. Its strains can be developed as host-specific, considering their broad-spectrum as


#### **Table 2.**

*Summary of some studies on the control of cotton pests using* Beauveria bassiana.

an insect pathogen [57]. *B. bassiana* has good control by coming into contact with the insect pests [58]. *B. bassiana* attacks its host by penetrating the exoskeleton or cuticle [59], producing a toxin that prevents the immune response of the host [52]. Even though *B. bassiana* based biopesticides may reduce the application of chemical pesticides; their effectiveness requires enhanced formulation or combining them with other pesticides [60]. *B. bassiana* is a promising pathogen against a variety of cotton pests, including spider mites [61], stainers [62], thrips [63], whiteflies [64, 65], aphids and bollworms [52, 54]. Some research on the efficacy of *B. bassiana* on cotton pests are documented in **Table 2**.
